Vpliv požara na obnašanje ojačanih betonskih linijskih konstrukcij

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Language:	Slovenian
Year of publishing:	2008
Source:	Ljubljana
Typology:	2.08 - Doctoral Dissertation
Organization:	UL FGG - Faculty of Civil and Geodetic Engineering
Publisher:	[N. Krauberger]
UDC:	614.84:624.012.46(043.3)
COBISS:	4067169
Views:	2356
Downloads:	818
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Secondary language:	English
Secondary title:	Analysis of prestressed concrete structures exposed to fire
Secondary abstract:	The thesis presents the mathematical model and numerical procedure for geometrically and materially non-linear static analysis and fire resistance of prestressed concrete structures. The mathematical model is limited to pretensioned prestressed concrete structure. In the derivation of matematical model the slip effect between concrete part of the structure and prestressing steel is considered, while the concrete spalling is not included into the matematical model. Because the problem was very complex we decided to divide the thesis into two parts. The first part presents the static analysis and the system of fundamental equations of prestressed concrete structures considering slip effect between concrete part of structure and prestressing steel. Reissner’s planar beam theory is used to model the concrete part of the structure, while the prestressing steel is modelled as a rope model. The system of the fundamental equations has to be solved numerically. Therefore, a modified principle of virtual work is used to derive the strain based family of finite elements for a non-linear analysis of prestressed concrete structures. The applicability and the accuracy of the proposed mathematical model and numerical procedure of prestressed concrete structures subjected to static load are illustrated and verified by numerical examples avaliable in literature. It was found out that the slip effect between concrete part of the structure and prestressing steel has a significant influence on kinematic and static quantities in prestressed concrete structures. In the second part, which is the main part of the thesis the mathematical model and numerical procedure is expanded to the analysis of prestressed concrete structure exposed to fire. Because the problem is very complex, the problem was devided into two phases. In the first phase the temperature and moisture content in concrete section are analysed. The Luikov matematical model with two coupled non-linear partial differential equations is used to describe the simultaneous heat and moisture content. Material parameters are dependent on temperature and moisture content. Generally, the exact solution of this problem is not known, therefore the simultaneous heat and moisture content in porous material has to be solved numerically. In our case the finite difference method is used. The temperature field of the structure represents the temperature load in the second phase of the analysis, where the mechanical response of prestressed concrete structures simultaneously exposed to static load and fire is presented. Concrete, reinforcing and prestressing steel all depend on temperature. Also, the slip-shear stress relationship between concrete part of the structure and prestressing steel depend on temperature. The geometric strain increment is assumed to be the sum of increments of elastic, plastic, temperature and creep strain in concrete, reinforcing steel and prestressing steel and the increment of trainsent strain in concrete. The applicability and the accuracy of prestressed concrete structures subjected to static load and fire is illustrated and verified by numerical examples avaliable in literature. It was found out that simultaneous heat and moisture content has an important influence on the temperature and moisture content analysis in concrete. It was also found out that the slip effect between concrete part of the structure and prestressing steel significantly affects on the stress and strain state of prestressed concrete structures, when taken into account.
Secondary keywords:	prestressed concrete beams;slip;contact concrete-prestressing steel;Reissner's beam theory;fire resistance;finite difference method;creep;finite element method;
URN:	http://www.dlib.si/?urn=URN:NBN:SI:doc-28187CBW
File type:	application/pdf
Type (COBISS):	Dissertation
Thesis comment:	Univ. v Ljubljani, Fak. za gradbeništvo in geodezijo
Pages:	XXVIII, 109 str.
Type (ePrints):	thesis
Title (ePrints):	Analysis of prestressed concrete structures exposed to fire
Keywords (ePrints):	prednapeti betonski nosilci;zamik;stik beton-jeklo za prednapenjanje;Reissnerjev nosilec;požarna odpornost;lezenje;diferenčna metoda;metoda končnih elementov
Keywords (ePrints, secondary language):	prestressed concrete beams;slip;contact concrete-prestressing steel;Reissner’s beam theory;fire resistance;finite difference method;creep;finite element method
Abstract (ePrints):	V disertaciji je predstavljen matematični model in računski postopek za geometrijsko in materialno nelinearno analizo predhodno napetih betonskih linijskih konstrukcij ob sočasnem delovanju mehanske in požarne obtežbe. Pri izpeljavi modela so upoštevani zamiki na stiku med betonom in jeklom za prednapenjanje, luščenje betona pa v modelu ni upoštevano. Zaradi zahtevnosti modela je vsebina disertacije razdeljena na dva dela. V prvem delu so predstavljene osnovne enačbe modela za analizo prednapetih betonskih linijskih konstrukcij pri sobni temperaturi. Obnašanje betonskega dela prednapete linijske konstrukcije je opisano z Reissnerjevim modelom ravninskega nosilca, obnašanje jekla za prednapenjanje pa z modelom vrvi. Osnovne enačbe modela so rešene s pomočjo novih deformacijskih končnih elementov, ki so izpeljani s pomočjo modificiranega izreka o virtualnem delu. Ustreznost in natančnost predstavljenega matematičnega modela in računskega postopka za analizo prednapetih betonskih linijskih konstrukcij pri sobni temperaturi je ocenjena s primerjavo med numeričnimi in eksperimentalnimi rezultati. Primerjava je pokazala, da togost stika med betonom in jeklom za prednapenjanje bistveno vpliva na potek kinematičnih in statičnih količin v prednapetih betonskih linijskih konstrukcijah. V drugem delu naloge, ki je tudi osrednja tema disertacije, je matematični model in računski postopek za analizo prednapetih betonskih linijskih konstrukcij pri sobni temperaturi razširjen na razmere, ki vladajo med požarom. Predstavljeni model je razdeljen na dve matematično nepovezani fazi. V prvi fazi je določena časovna in krajevna razporeditev temperature in vlage v prečnem prerezu prednapete betonske linijske konstrukcije. Za opis povezanega prenosa toplote in vlage v kapilarno poroznih materialih med požarom je uporabljen Luikov matematični model. Določata ga dve povezani nelinearni parcialni diferencialni enačbi s temperaturno in vlažnostno odvisnimi materialnimi parametri. Enačbi sta rešeni z diferenčno metodo. V drugi fazi analize je s pomočjo dobljenih rezultatov prve faze določen časovni odziv prednapete linijske konstrukcije med požarom ob sočasnem delovanju mehanske in temperaturne obtežbe. Materialni zakoni betona, jekla za armiranje in jekla za prednapenjanje so nelinearni, pripadajoči materialni parametri pa so odvisni od temperature. Prav tako je nelinearna in odvisna od temperature konstitucijska zveza med zamiki in strižnimi napetostmi na stiku med betonom in jeklom za prednapenjanje. Pri določitvi napetostnega in deformacijskega stanja prednapetih linijskih konstrukcij med požarom so poleg mehanskih in temperaturnih deformacij upoštevane tudi t.i. prehodne deformacije betona in lezenje betona ter viskozno lezenje jekla za armiranje in prednapenjanje. Ustreznost in natančnost predstavljenega matematičnega modela in računskega postopka za analizo prednapetih betonskih linijskih konstrukcij med požarom je ocenjena s primerjavo med numeričnimi in eksperimentalnimi rezultati. Primerjava in podrobna parametrična študija je pokazala, da je časovno in krajevno razporeditev temperatur in vlage v prednapetih linijskih konstrukcijah potrebno določiti z enačbami povezanega prenosa toplote in vlage, ter da imajo zamiki na stiku med betonom in jeklom za prednapenjanje pomemben vpliv na napetostno in deformacijsko stanje ter požarno odpornost prednapetih betonskih linijskih konstrukcij in jih v analizi ne smemo zanemariti.
Abstract (ePrints, secondary language):	The thesis presents the mathematical model and numerical procedure for geometrically and materially non-linear static analysis and fire resistance of prestressed concrete structures. The mathematical model is limited to pretensioned prestressed concrete structure. In the derivation of matematical model the slip effect between concrete part of the structure and prestressing steel is considered, while the concrete spalling is not included into the matematical model. Because the problem was very complex we decided to divide the thesis into two parts. The first part presents the static analysis and the system of fundamental equations of prestressed concrete structures considering slip effect between concrete part of structure and prestressing steel. Reissner’s planar beam theory is used to model the concrete part of the structure, while the prestressing steel is modelled as a rope model. The system of the fundamental equations has to be solved numerically. Therefore, a modified principle of virtual work is used to derive the strain based family of finite elements for a non-linear analysis of prestressed concrete structures. The applicability and the accuracy of the proposed mathematical model and numerical procedure of prestressed concrete structures subjected to static load are illustrated and verified by numerical examples avaliable in literature. It was found out that the slip effect between concrete part of the structure and prestressing steel has a significant influence on kinematic and static quantities in prestressed concrete structures. In the second part, which is the main part of the thesis the mathematical model and numerical procedure is expanded to the analysis of prestressed concrete structure exposed to fire. Because the problem is very complex, the problem was devided into two phases. In the first phase the temperature and moisture content in concrete section are analysed. The Luikov matematical model with two coupled non-linear partial differential equations is used to describe the simultaneous heat and moisture content. Material parameters are dependent on temperature and moisture content. Generally, the exact solution of this problem is not known, therefore the simultaneous heat and moisture content in porous material has to be solved numerically. In our case the finite difference method is used. The temperature field of the structure represents the temperature load in the second phase of the analysis, where the mechanical response of prestressed concrete structures simultaneously exposed to static load and fire is presented. Concrete, reinforcing and prestressing steel all depend on temperature. Also, the slip-shear stress relationship between concrete part of the structure and prestressing steel depend on temperature. The geometric strain increment is assumed to be the sum of increments of elastic, plastic, temperature and creep strain in concrete, reinforcing steel and prestressing steel and the increment of trainsent strain in concrete. The applicability and the accuracy of prestressed concrete structures subjected to static load and fire is illustrated and verified by numerical examples avaliable in literature. It was found out that simultaneous heat and moisture content has an important influence on the temperature and moisture content analysis in concrete. It was also found out that the slip effect between concrete part of the structure and prestressing steel significantly affects on the stress and strain state of prestressed concrete structures, when taken into account.
Keywords (ePrints, secondary language):	prestressed concrete beams;slip;contact concrete-prestressing steel;Reissner’s beam theory;fire resistance;finite difference method;creep;finite element method
ID:	8311991